Tuesday, March 25, 2014

Young Crater Walls (at the Schrödinger Antipode)

Northern rim of an unnamed young crater near 80°N, 278.9°E, north of Catena Sylvester, on the far north nearside and nested within crustal magnetism that may be related to the Moon's youngest impact basin (Schrödinger) on the direct opposite side of the Moon. 1243 meter-wide field of view, sampled from LROC Narrow Angle Camera observation M125130801R, LRO orbit 3574, April 5, 2010; 78.42° incidence, 1.09 meters resolution from 53 km [NASA/GSFC/Arizona State University].].

Hiroyuki Sato
LROC News System

After the unimaginably violent processes of excavation and ejecta emplacement, impact craters gradually change their shapes with time by various processes, such as the isostatic rebound, mass wasting, subsequent impacts, and space weathering.

Today's Featured Image highlights such a post-impact degradation process.

Full-width mosaic of the LROC NAC observation from orbit 3574. The full-sized (4581 x 6319) original can be viewed HERE. Though the high-angle of illumination at this high latitude favors outlines of topography over intrinsic brightness and color, relatively darker and lighter materials radiate over great distances, aiding studies of how younger materials interact with anomalous local magnetism [NASA/GSFC/Arizona State University].

The lower half of this image (relatively high reflectance) is the crater wall, downslope is to the bottom. The bottom-left dark area is the shadow of southern crater rim. Upper half of the image with a low reflectance surface is the crater rim and the rim slope out of the cavity, mostly covered with impact melt. The low reflectance area at the image center just above the steep wall has multiple horizontal cracks showing where the hardened impact melt has cracked as the steep walls slowly fail and slide into the crater bit-by-bit. These slope failures continuously refresh the crater walls, removing the melt coatings and exposing subsurface materials.

Context image of the unnamed crater and the surrounding area in LROC WAC monochrome mosaic (100 m/pix). Image center is 79.97°N, 278.87°E; image width is about 66 km. The NAC footprint and the location of the opening image are illustrated [NASA/GSFC/Arizona State University].

Most of the fresh craters that we observe have suffered these slides, leaving the commonly observed rootless melt flow features on the rim slopes. Just after the impact occurred, much of the crater interior was covered by impact melt, but these rock veneers are quickly removed from steep slopes leaving fresh outcrops of the target (regolith and, in the case of mare, bedrock).

Arrow marks the young crater highlighted in the LROC Featured Image, released March 25, 2014, west of Poncelet C. The white circle is an approximate reflection of the parameters of the Schrödinger impact basin, the Moon's youngest, centered on a point on the diametrically opposite (antipodal) side of the Moon from the center of Schrödinger, in the far south. Grey lines outline nodes of anomalous crustal magnetism teased from Lunar Prospector (1998-99) data. Noted planetary scientists Lon Hood and Paul Spudis use the excavation caused by the smaller impact to aid in determining how local topography may have been disrupted, as they have suggested, by the force of the Schrödinger basin-forming impact. One challenge will be to determine how much the comparatively weak crustal magnetism interacts with migrating dust and fresh impact debris to create albedo swirl features [NASA/GSFC/Arizona State University].